Effect of hypoxia on the maintained firing rate of retinal ganglion cells.

The effect of systemic hypoxia on the maintained firing rate (MFR) of single retinal ganglion cells has been measured in the cat at a constant luminance level. Systemic hypoxia was produced by reducing the percentage of oxygen in the respiratory mixture under forced ventilation so that arterial PCO2 and pH were constant. Extracellular recordings were obtained from both X and Y retinal ganglion cells before, during, and after systemic hypoxia, with each cell acting as its own control. The MFR was unaltered by arterial PO2 levels of greater than 45 mm Hg. However, at and below this level of hypoxia the MFR was reversibly increased in 67% of the cells tested. Whether or not this increase occurred was independent of cell type or location. For arterial PO2 values of 24 to 34 mm Hg the initial increase in MFR was followed by a decrease for these cells; for PO2 values of less than 24 mm Hg the MFR showed a large initial increase followed by a complete cessation of firing. The remaining 33% of cells displayed only reduced MFR during hypoxia. The results indicate that ganglion cell function may be drastically affected by hypoxia. This may be relevant to the visual loss of a variety of retinal disorders.